1. Field of the Invention
The present invention relates to a bend-detecting sensor (hereinafter referred to as "bending sensor") which is used for detecting bent or deformed portions of machines and tools and bending-angles of human bodies' joints.
2. Description of Prior Art
It has been conventionally known an electric-resistance strain gauge as means to measure a degree and distribution of stress and load formed at a part of a machine or a structure, and deformed state of mechanical components and the like. There have been known various kinds of methods and machines used for the measurement of strain. Among them, it has been said that measuring means using a strain gauge is most accurate means.
In the strain gauge, a metal-resistance body which is photo-optically etched is bonded on a film-shaped resin and a leading wire is drawn out of the metal-resistance body. Strain which occurs in a substance to be measured is converted into change in resistance to be outputted. In other words, strains ocurring in the substance to be measured are transferred to the metal-resistance body via the film-shaped resin which is a base, and the metal-resistance body is deformed in response to the degree of strain, causing change in resistance, which is taken out as an output. The output of the strain gauge is detected by, for example, Wheatstone bridge circuit and "strain amount" caused in a substance to be measured is calculated by the output voltage of the Wheatstone bridge circuit. The strain gauge is used for industrially testing the strength of a material and for analysis in structure-mechanism of civil engineering and construction, and used as elements of various kinds of transducers and as sensors of control machines or tools in an automobile.
The principle of the strain sensor is utilized for detecting movement of a human body or a movement of a finger. For example, Japanese Patent Application Laid-open No. Hei 4-233442 (JP-A-4-233442) discloses a bending sensor which comprises an elastic body and has a construction such that a resistance-body is provided inside the elastic body and a neutral face at bending of the resistance-body and a neutral face at bending of the elastic body are placed in the vicinity where the both neutral faces do not coincide.
The resistance-body used in the invention of the Japanese Patent Application Laid-open No. Hei 4-233442 is identical with the metal-resistance body of the aforesaid strain sensor. The bending sensor is set on a necessary part of a body of a player who plays a piano, a guitar, etc. When the player' body is bent, the bending sensor detects the bending-degree and generates detecting signals. The detecting signals are outputted to the outside. As one of an application of the bending sensor, for example, there is a wearing tool in a form of a glove in which each bending sensor is fitted to the backface of each finger of the glove. When a player wearing the fitting tool performs a music in a musical instrument, a detected output as to how fingers are moved at the musical performance can be obtained.
However, the above-described bending-sensor has such problems that the metal-resistance body which is used for detecting the bending of a substance to be measured is not necessarily great in regard to an amount of change in resistance by strain and that when bending-deformation is repeated to the metal-resistance body, the life of the resistance-change is lowered by metal fatigue due to the fact that the metal-resistance body is made of a metal. Japanese Patent Application Laid-open No. Hei 4-233442 intends to reduce the metal fatigue of its sensor by relatively largely setting the shift of positions of the neutral face at bending of the resistance body and the neutral face at bending of the elastic body so as to reduce the strain amount. However, even though the metal fatigue is reduced, it is only a degree of reduction.
The problem of metal fatigue has not be solved fundamentally. As contrast from Japanese Patent Application Laid-open No. Hei 4-233442 in which the metal resistance body is adhered to the base member by an adhesive, the metal resistance body can be formed on the base member by using sputtering method.
However, the sputtering method requires high technology and in any way, as long as the sensor uses a metal-resistance body, metal fatigue is generated; and unless this problem is not solved, the sensor made of a metal material is not necessarily effective for detecting a large bending.